The word "scaffolding" is borrowed from the construction industry, originally meaning "scaffolding", which refers to the temporary structure used to build or transform buildings [1]. Bruner, an American psychologist, first used scaffolding in the field of learning, referring to temporary support for learners, which can help them complete tasks that cannot be completed alone [2]. The theoretical basis of scaffolding instruction comes from Vygotsky's "zone of proximal development". Vygotsky believes that there is a gap between the current level and the potential level of students, which is called the "zone of proximal development". "Scaffolding" is considered as a cognitive tool, which can promote students' current level to potential level in the children's recent development area. Using scaffolding in classroom teaching can effectively promote students' cognitive development and improve their autonomous learning ability. However, at present, few studies provide theoretical guidance for scaffolding classroom teaching practice. By analyzing the practical characteristics of scaffolding instruction, this paper discusses the main challenges faced by scaffolding classroom instruction, and puts forward corresponding suggestions, so as to provide some reference for the vast number of educational theories and practitioners to study and apply scaffolding instruction. Practical characteristics of scaffolding instruction in 1

As a teaching paradigm gestated under the constructivism theory, scaffolding instruction embodies an operation paradigm different from traditional teaching: choosing scaffolding around "specific theme", embodying the teaching process of "from helping to releasing", and realizing the responsibility transfer from teachers to students.

1. 1 Select the brackets around "specific topic"

Teachers provide students with many kinds of scaffolding, such as questions, hints, explanations, demonstrations, encouragement, charts and so on. What kind of scaffolding to use needs teachers to make a comprehensive decision according to the teaching content, teaching objectives and students' performance. Because of the complexity and uncertainty of students' cognitive process,

Teachers can't determine the type of scaffolding students need in advance, so they need to choose specific teaching topics. Different subjects have different teaching themes, and the same subject also has different teaching subjects, such as Chinese reading and writing, mathematics geometry and algebra. In addition, the same theme is not limited to the use of a scaffold. Teachers can choose suitable scaffolding according to different links of teaching design, thus ensuring the smooth progress of teaching.

1.2 embodies the teaching process of "from support to release"

"From support to release" means that with the enhancement of students' ability, the scaffolding built for students is gradually dismantled. Support for students includes the number and degree of support. The number of stents is the total number of stents provided to students. The degree of support of scaffolding refers to the degree of support for students' cognitive activities when facing the same learning tasks. Taking teaching students how to solve mathematical application problems as an example, it is stronger to provide students with general problem-solving strategies than to only imply that students support how to solve problems. In the early stage of teaching, because students have just come into contact with new knowledge, their adaptability to knowledge is weak. Therefore, teachers provide students with more scaffolding and stronger support. As students become more familiar with new knowledge and have stronger adaptability, teachers can gradually reduce the number and support of scaffolding, and finally enable students to complete their learning tasks independently without the help of teachers.

1.3 to realize the responsibility transfer from teachers to students

The transfer of responsibility is closely related to the gradual withdrawal of scaffolding. "Through the gradual retirement of scaffolding, the responsibility of learning tasks is gradually transferred to learners." [1] The gradual reduction of scaffolding not only means the gradual reduction of teachers' support for students, but also means that the role of teachers has changed since the beginning of learning.